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Home / DTC / U0669 — Lost Communication With EGR Sensor D

U0669 — Lost Communication With EGR Sensor D

Detailed page for trouble code U0669.

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Code

U0669

Generic U — Network/User

Lost Communication With EGR Sensor D

Brand: Generic
Type: U — Network/User
Views: UK: 13 EN: 34 RU: 14
AI status
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Page language: EN

Causes

  • Open or shorted wiring between the EGR sensor D and PCM
  • Corroded, loose, or damaged connector at sensor or PCM
  • Faulty EGR sensor D (internal electronics/processor)
  • CAN/serial bus fault (bus off, termination, high/low short)
  • Blown fuse or missing power/ground to the sensor or related module
  • PCM/ECM software fault or internal failure

Symptoms

  • Malfunction Indicator Lamp (MIL) illuminated
  • Related EGR system functions disabled or defaulted (may affect emissions)
  • Engine may run less efficiently; possible rough idle or reduced performance
  • Failed emissions test or elevated NOx readings
  • Stored U0669 sometimes accompanied by other communication codes

What to check

  • Scan for stored and pending codes and freeze-frame data; note time and operating conditions
  • Check for additional U‑codes or CAN bus errors on the scanner
  • Visually inspect sensor connector and wiring for corrosion, damage, or water
  • Verify fuses and power/ground circuits for the EGR sensor circuit
  • With ignition on, measure reference voltage and ground at the sensor connector
  • Check CAN bus wiring for damage and measure idle voltages on CAN High and CAN Low

Signal parameters

  • Sensor communication: typically a low-speed serial or CAN data message; expected regular messages from sensor to PCM
  • CAN bus idle voltages: CAN_H ≈ 2.5 V and CAN_L ≈ 2.5 V (use oscilloscope to confirm differential signaling activity)
  • Reference supply: sensor may use 5 V reference (verify with meter)
  • Ground integrity: near 0 V between sensor ground and vehicle chassis
  • Expected message rate: periodic messages; absence or irregular timing indicates fault (check with scan tool)

Diagnostic algorithm

  1. Connect a professional scan tool and record U0669 plus any related codes and freeze-frame data
  2. Perform a visual inspection of EGR Sensor D connector, wiring, and PCM connector for corrosion, bent pins, or water intrusion
  3. Verify power and ground at the sensor connector with ignition ON (compare to vehicle wiring diagram for correct circuits and expected voltages)
  4. Check continuity between sensor connector pins and the PCM connector for data, power and ground; repair any opens or high resistance
  5. Inspect CAN/serial bus: measure CAN_H and CAN_L with oscilloscope while cranking/running; look for expected idle voltages and message activity
  6. Perform a wiggle test on harness and connectors while monitoring the scan tool for communication dropouts
  7. If wiring and power/ground are good, substitute a known-good EGR sensor (if available) or bench-test the sensor according to manufacturer procedure
  8. If replacement sensor does not restore communication, check for other modules pulling the bus down or causing bus-off; isolate segments and retest
  9. If wiring and sensor check good, consider reprogramming/updating PCM software per technical service bulletins or consult manufacturer for module diagnostics
  10. After repairs, clear codes and perform a road/drive cycle to ensure code does not return and EGR operation is restored

Likely causes

  • Damaged connector or corroded pins at the EGR sensor
  • Broken or shorted harness conductor between sensor and PCM
  • Faulty EGR sensor D electronics
  • Loss of reference power or ground to the sensor
  • CAN bus fault or another module pulling the bus down

Fault status

⚠️ Status
Lost serial/CAN communication between PCM and EGR Sensor D. PCM did not receive expected sensor messages; fault may be intermittent or permanent and can be caused by wiring, connector, sensor, or bus faults.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

U0100 U0073 U0121 U0141
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